Inhibition of PAF synthesis by stimulated human polymorphonuclear leucocytes with cloricromene, an inhibitor of phospholipase A2 activation

Retinal and Systemic Pharmacokinetics of the Anti-Inflammatory Drug Cloricromene Following Oral Administration in the Rat and Rabbit

PURPOSE

The aim of this study was to evaluate the retina and plasma distribution of cloricromene, a coumarin derivative, and its active metabolite (MET) after an oral administration in rabbits and rats.

METHODS

A single dose of cloricromene was orally administered to rabbits (10 or 100 mg/kg) and to rats (100 mg/kg). Retina and plasma samples were collected at 15, 30, 60, and 90 min following administration. Drug concentrations in the retina and plasma were measured by high-performance liquid chromatography.

RESULTS

As anticipated, only the active metabolite was found in all samples. The retina and plasma showed the same T(max); peak levels of the drug were achieved at 15 min in rats and at 30 min in rabbits. In rabbits, MET exposure was approximately dose-proportional in both retina and plasma between the 10- and 100-mg/kg dose. Substantial retinal exposure was observed in both the rat and rabbit, at exposures approximately nine- to sixteenfold lower in the retina than in plasma.

CONCLUSIONS

The results showed that the active metabolite of cloricromene reached the retina after a single oral dose with exposures proportional to those in plasma. These data, along with the previously published potency data for cloricromene, suggest that cloricromene could be potentially useful in ischemic-retinal diseases where amelioration of blood flow and inflammation is desirable.

A protective effect of the synthetic coumarine derivative Cloricromene against DNB-colitis in the rat

Biologic therapies, namely antibodies against tumor necrosis factor-alpha (TNF- alpha) or its receptors, have been recently introduced for the treatment of patients with inflammatory bowel disease (IBD). In the present study the effects of cloricromene, an agent with known antithrombotic actions and with demonstrated anti-TNF- alpha activity were investigated in a rat model of experimental colitis induced with dinitrobenzenesulphonic acid (DNB)/ethanol. We investigated three experimental groups: (i) sham-colitis with vehicle-treatment (controls, n = 6), (ii) colitis with vehicle-treatment (saline, 0.1 ml s.c., daily) (DNB-V, n = 7), (iii) colitis with cloricromene-treatment (10 mg/kg/day s.c.; DNB-C, n = 8). After 7 days, the weight gain, colon wet weight, macroscopic damage score, coagulation parameters, colon mucosal myeloperoxidase activity (MPO), and tissue concentrations of TNF- alpha and of macrophage inhibitory peptide-2 (MIP-2) were assessed. The macroscopic damage scores, colon wet weights, and tissue MIP-2 levels were significantly increased in untreated and in cloricromene-treated rats compared with controls. Cloricromene treatment was associated with a minor body weight loss (p < 0.025) and significantly reduced tissue concentrations of MPO and TNF-alpha (p < 0.02, both). Blood coagulation parameters were not affected by treatment. In the DNB-model treatment with cloricromene effectively reduces tissue levels of TNF- alpha and of myeloperoxidase, whereas MIP-2 concentrations were not influenced. Blood coagulation parameters remained unchanged indicating safety of treatment. Since biological therapies frequently fail to improve disease course of IBD, other therapies with similar targets should be further investigated.

Simultaneous determination of cloricromene and its active metabolite in rabbit aqueous humor by high-performance liquid chromatography

A rapid and simple method was developed for the simultaneous separation and quantification of cloricromene, a coumarine derivative, and its active metabolite, cloricromene acid, in rabbit aqueous humor. The analyses were performed by high-performance liquid chromatography using a C18 reversed-phase column (Hypersil ODS) with UV detection at 318 nm. The mobile phase consisted of acetonitrile-water containing 1% triethylamine pH 3.5, adjusted with orthophosphoric acid. An acetonitrile gradient was necessary to achieve good separation within 13 min. Timolol was found to be a suitable internal standard. The retention times ranged from 5.72 to 11.25 min. A simple pre-treatment with acetonitrile containing 0.6% HCIO4 was used to deproteinize aqueous humor samples. The limit of quantitation ranged between 10 and 20 ng/ml. The recovery was >90%. The relationship between peak areas and concentration was linear over the range between 0.01 and 3.8 microg/ml, with r2 > 0.99. The assay provided good reproducibility and accuracy for both analytes and proved to be suitable for pharmacokinetic studies of cloricromene.

Cloricromene, a semi-synthetic coumarin derivative, inhibits tumor necrosis factor-alpha production at a pre-transcriptional level

Cloricromene decreases myocardial infarct size after ischemic-reperfusion injury in vivo, and it has been suggested that this is due to inhibition of tumor necrosis factor-alpha (TNF-alpha). The purpose of this work was to characterize the mechanism of cloricromene-induced inhibition of TNF-alpha in rat macrophages. Cloricromene inhibited lipopolysaccharide-induced TNF-alpha release in a dose-dependent manner (IC(50)=5.9 +/- 0.8 microM). This was not due to cytotoxicity, as cloricromene was well tolerated up to 500 microM. Cloricromene inhibited lipopolysaccharide-induced expression of TNF-alpha mRNA, which suggests a pre-transcriptional effect. We then investigated the early signal transduction pathway triggered by lipopolysaccharide. The binding of lipopolysaccharide to its receptor CD14 activates protein kinase C and nuclear factor-kappaB (NF-kappaB). Cloricromene inhibited NF-kappaB activation in a dose-dependent manner, but affected protein kinase C translocation only slightly. We then established that cloricromene inhibited lipopolysaccharide-induced cellular oxidative activity, which is important for NF-kappaB activation. Our results show that cloricromene interferes with the early signal transduction pathway triggered by lipopolysaccharide.

Effect of cloricromene on intermittent claudication. A randomized, double-blind, placebo-controlled trial in patients treated with aspirin: effect on claudication distance and quality of life. CRAMPS Investigator Group. Cloricromene Randomized Arteriopathy Multicenter Prospective Study

The main aim of medical treatment for intermittent claudication (IC) is the reduction of mortality and morbidity from ischemic cardiovascular disease. However, symptomatic treatment with the aim of improving exercise performance and the overall quality of life may also be an important target of the clinical management of patients with intermittent claudication. Cloricromene, a drug with antithrombotic and anti-ischemic activities, has previously shown some promising results in patients with claudication. We have carried out a clinical trial to assess the effect of cloricromene on the claudication distance and on the quality of life of patients with IC chronically treated with aspirin. A total of 159 patients with IC, Stage II (Fontaine), were enrolled in a double-blind, randomized, prospective, multicenter study comparing cloricromene (100 mg orally b.i.d.) or an identical placebo for 6 months. All patients received 160 mg/day aspirin. The primary end-point was the improvement of initial claudication distance (ICD) at 6 months as measured by a standardized treadmill test. The secondary end-points were the absolute claudication distance (ACD) at 6 months, the percentage of patients defined as responders to treatment (improvement of ICD of at least 40%), changes in the ischemic window (IW), quality of life as assessed by the SF-36 questionnaire, and the occurrence of major cardiovascular events. The ICD increased in both treatment groups, with a non-significant difference at 6 months in favor of cloricromene of +12.3 m. The ACD, percentage of responders to treatment and ischemic window also improved in both groups with a slight, non-significant trend in favor of cloricromene. Pretreatment quality of life scores showed only a slight worsening compared with an age-matched, healthy population and did not change upon treatment. A post hoc subgroup analysis showed a significant benefit from cloricromene in patients with an ICD at enrollment higher than the median of the patient population. In conclusion, treatment with cloricromene for 6 months does not significantly improve claudication in patients with Stage II Fontaine peripheral arteriopathy chronically treated with aspirin. An improvement of 40-60 m in the ICD on a standardized treadmill test does not translate into a self-perceived improvement in the quality of life as assessed by the SF-36 questionnaire.

Sera of patients suffering from inflammatory diseases contain group IIA but not group V phospholipase A(2)

During recent years, the high phospholipase A(2) (PLA(2)) concentrations at sites of inflammation and in circulation in several life-threatening diseases, such as sepsis, multi-organ dysfunction and acute respiratory distress syndrome, has generally been ascribed to the non-pancreatic group IIA PLA(2). Recently the family of secreted low molecular mass PLA(2) enzymes has rapidly expanded. In some cases, a newly described enzyme appeared to be cross-reactive with antibodies against the group IIA enzyme. For this reason, reports describing the expression of group IIA PLA(2) during inflammatory conditions need to be reevaluated. Here we describe the identification of the PLA(2) activity in sera of acute chest syndrome patients and in sera of trauma victims. In both cases, the PLA(2) activity was identified as group IIA. This classification was based upon cross-reactivity with monoclonal antibodies against group IIA PLA(2) which do not recognize the recombinant human group V enzyme. Moreover, purification of the enzymatic activity from the two sera followed by N-terminal amino acid sequence analyses revealed only the presence of group IIA enzyme.

Platelet-activating factor contributes to acute lung leak in rats given interleukin-1 intratracheally

Lung lavage fluid of patients with acute lung injury (ALI) has increased levels of interleukin-1 (IL-1) and neutrophils, but their relationship to the lung leak that characterizes these patients is unclear. To address this concern, we investigated the role of the neutrophil agonist platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF)] in the development of the acute neutrophil-dependent lung leak that is induced by giving IL-1 intratracheally to rats. We found that PAF acetyltransferase and PAF activities increased in lungs of rats given IL-1 intratracheally compared with lungs of sham-treated rats given saline intratracheally. The participation of PAF in the development of lung leak and lung neutrophil accumulation after IL-1 administration was suggested when treatment with WEB-2086, a commonly used PAF-receptor antagonist, decreased lung leak, lung myeloperoxidase activity, and lung lavage fluid neutrophil increases in rats given IL-1 intratracheally. Additionally, neutrophils recovered from the lung lavage fluid of rats given IL-1 intratracheally reduced more nitro blue tetrazolium (NBT) in vitro than neutrophils recovered from control rats or rats that had been given WEB-2086 and then IL-1. Histological examination indicated that the endothelial cell-neutrophil interfaces of cerium chloride-stained lung sections of rats given IL-1 contained increased cerium perhydroxide (the reaction product of cerium chloride with hydrogen peroxide) compared with lungs of control rats or rats treated with WEB-2086 and then given IL-1 intratracheally. These in vivo findings were supported by parallel findings showing that WEB-2086 treatment decreased neutrophil adhesion to IL-1-treated cultured endothelial cells in vitro. We concluded that PAF contributes to neutrophil recruitment and neutrophil activation in lungs of rats given IL-1 intratracheally.

Differential inhibition of polymorphonuclear leucocyte functions by cloricromene

Leucocytes play an essential role in the pathogenesis of ischaemia and reperfusion injury and inhibition of their adhesion and of mediator release can reduce vascular and tissue damage. Previous studies have shown that cloricromene modifies several granulocyte as well as monocyte/macrophage functions and it has been shown that cloricromene administration exerts a clear protective action in several experimental models of ischaemia. The present work describes new data on polymorphonuclear leukocyte (PMN) inhibition exerted by cloricromene and compares these observations with earlier ones. Human washed PMN and human whole blood (HWB) were studied in vitro upon stimulation with f-MLP in the presence of cytochalasin B, with opsonized zymosan and with a phorbol ester (PMA). Amongst free radicals, superoxide anions were chosen as index of oxidative burst. Phagocytosis and beta-glucuronidase, as lysosomal release indicators, were measured to characterize PMN function: cloricromene inhibited concentration-dependently all the parameters upon stimulation by each activator tested. Experiments performed in rabbit whole blood (RWB) showed that cloricromene inhibited free radical generation with IC50 values similar to those obtained in human whole blood. Comparing the action of cloricromene on human cells in different tests, we found that some parameters were more sensitive than others, even when the same stimulus was used. In particular, free radical generation was inhibited by cloricromene with IC50 values below 36 microM, while other functions, like lysosomal release and phagocytosis were inhibited with IC50 values over 100 microM. These data confirm that cloricromene exerts a notable inhibitory effect on PMN and may explain the activity of the compound, observed in vivo in several experimental models of ischaemia-reperfusion and shock.

Regulation of platelet-activating factor (PAF) activity in human diseases by phospholipase A2 inhibitors, PAF acetylhydrolases, PAF receptor antagonists and free radical scavengers

The aim of this review is to present recent findings indicating the likely involvement of platelet-activating factor (PAF) in human diseases, and possible ways of alleviating its harmful effects. PAF is a potent proinflammatory mediator and promotes adhesive interactions between leukocytes and endothelial cells, leading to transendothelial migration of leukocytes, by a process of juxtacrine intercellular signalling. This process leads to activation of leukocytes and the release of reactive oxygen radicals, lipid mediators, cytokines and enzymes. These reaction products subsequently contribute to the pathological features of various inflammatory diseases. The reactive oxygen radicals cause low density lipoprotein (LDL) oxidation which mediates the development of atherosclerosis. Oxidized LDL may damage cellular and subcellular membranes, leading to tissue injury and cell death. Among the therapeutic approaches considered are agents that inhibit/degrade proinflammatory mediators and thereby have anti-inflammatory and/or anti-atherogenic potential. These include inhibitors of phospholipase A2 activity, PAF-acetylhydrolases, PAF antagonists and free radical scavengers/antioxidants, the latter protecting against oxidized LDL-induced cytotoxicity.

PAF levels in saliva are regulated by inflammatory cells

Platelet activating factor (PAF), a powerful inflammatory phospholipid mediator, has been detected in normal human saliva and found to be increased in periodontitis. The cellular source of PAF in saliva is controversial although several data suggest an origin related to the presence of inflammatory cells. PAF levels in biological fluids are regulated by PAF-producing cells and by the PAF-degrading acetylhydrolase. Although in normal human saliva acetylhydrolase activity is very low, no information is available on the levels of this enzyme in inflammatory conditions of the mouth. The aim of our study was to assess the contribution of inflammatory cells to the levels of PAF in saliva in normal subjects and in patients with periodontitis. PAF was measured by radioimmunoassay (RIA) in mixed uncentrifuged saliva and in cell-free saliva from healthy subjects, before and after tooth brushing, and in patients with periodontitis. In healthy subjects PAF levels were significantly higher in whole saliva than in centifuged saliva (1.51 +/- 0.22 vs. 0.92 +/- 0.04 ng/ml, p < 0.0039). A significant increase in the amount of PAF was detected in whole saliva, but not in centifuged saliva, 2 h after tooth brushing. In patients with periodontitis PAF levels were not different from those of healthy individuals when using centrifuged saliva but were significantly higher when using whole, uncentrifuged saliva. Exogenous radiolabelled PAF was degraded much more rapidly by the saliva of periodontitis patients than by that of normal subjects. In conclusion, our study shows that inflammatory cells regulate the levels of PAF in saliva contributing to its production and degradation. The differential degradation of PAF in normal and inflammatory saliva highlights the absolute need of a series of methodological precautions when performing studies on salivary PAF.